Field of the Invention
This invention relates to a method for quenching heat treated metallic work pieces and to an apparatus for carrying out the method.
Description of the Related Art
In some of the known heat treatment systems, a high pressure gas quench subsystem is used to rapidly cool the metal work pieces from the heat treatment temperature. As shown in FIG. 1, the quenching subsystem includes an accumulator tank 1 that stores a large volume of the quenching gas at a high pressure. When the accumulator tank empties into the furnace or a standalone quenching chamber 2, the gas pressure in the furnace or the quench chamber, as the case may be, rises quickly to the desired quenching level.
In the case where the final quench pressure is high, e.g., on the order of about 20-30 bar, for example, many large accumulator tanks would be required, each storing gas at a pressure much higher than the final quenching pressure. Such tanks are expensive and take up a lot of space in the processing facility. The rapid filling of the furnace requires a large pipe and valve size to allow the furnace to reach the final quench pressure in a short time. In order to pressurize the large accumulator tanks to the required high pressures, a compressor system or very high pressure gas delivery system is sometimes employed. Both of those systems require additional energy to fill the tanks. That energy ultimately is wasted because it does not convert into useful energy in the furnace quenching process.
The main problems the invention is meant to address are summarized as follows.                1) Physical space used by high pressure backfill tank(s).        2) The compressor systems that charge these tanks to high pressures (up to 30 bar or more) have periodic maintenance issues with wear parts and also add unwanted energy into the process of furnace quenching.        3) If a compressor system is not used, the end user of the furnace equipment would have to change the bulk gas storage system in the facility and the high pressure gas delivery line from what would be typically a 10 bar or an 18 bar gas delivery system to at least a 30 bar gas delivery system.        4) Typically gas is kept in a liquid state in bulk storage systems. It takes energy to change the gas into a liquid form, energy that the end user already paid for when they bought the liquid gas. If the liquid gas is used downstream of the bulk storage system, it commonly goes through a vaporizer to turn it back into a gaseous state before delivery. The conversion of liquid gas to the gaseous state gives up stored energy by cooling the vaporizer. This energy is wasted and is not useful in the furnace quenching process.        